Variable displacement pump having pressure compensation control means

ABSTRACT

A variable displacement pump of the type having a plurality of rotatable, axially-aligned pistons guided by a pivotal swash plate for enabling adjustment of displacement and also having a sharp cutoff pressure compensator control means whereby the swash plate is shifted to its minimum displacement position when a predetermined maximum pressure is reached or when the pump load is in a neutral condition, thereby curtailing heat generation and horsepower loss.

United States Patent 1 Hein et al.

3,221,660 12/1965 DAmato ..4l7/ 222 ms 7R I32 .118 j" !26 72 4| 74% 38we Zgg- 76 68 1 80V 66 .g f/r 36 no s 40 VARIABLE DISPLACEMENT PUMPHAVING PRESSURE COMPENSATION CONTROL MEANS Inventors: Allyn J. Hein,Joliet; Walter Z.

Ruseff, New Lenox; Gilbert Tribley,

u.s. Cl. 417/213, 91/506 Int. Cl. F04b 49/00- Field of Search .1417/222, 238, 239,

References Cited UNITED STATES PATENTS June 12, 1973 2,291,424 7/1942Wichorek ..417/239 2,696,189 12/1954 Born et al. 91/505 PrimaryExaminer-William L. Freeh Assistant ExaminerGregory Paul LaPointeAttorney-Charles M. Fryer, Arnt H. Tjensvold, Paul S. Lempio et a1.

ABSTRACT 1 Claim, 3 Drawing Figures VARIABLE DISPLACEMENT PUMP HAVINGPRESSURE COMPENSATION CONTROL MEANS CROSS-REFERENCE TO RELATEDAPPLICATION Reference is made to copending application Ser. No. 157,535, filed June '28, 1971, assigned to the assignee of this invention,wherein is disclosed a similar device having variable-cutoff-pressurecompensator control means as opposed to the sharp cutoff pressurecompensator control means of the instant invention.

BRIEF SUMMARY This invention is directed to a variable displacement pumpof the type having a plurality of rotatable, axiallyaligned pistonsguided by a nonrotatable, tiltable swash plate which enables adjustmentof pump displacement by the operation of pressure compensator controlmeans.

Currently, constant displacement, as opposed to variable displacement,pumps are'widely used as a source of fluid pressue to power hydrauliccircuitsin many applications. For example, constant displacement pumpsare used to power hydraulic implement circuits on heavy constructionequipment such as tractors, etc. In this application there is noprovision for returning pump flow to tank when the implementcontrol-valves are in a neutral position unless an open-center system isused. However, with this type of system, an additional amount of enginehorsepower is needed to drive the constant delivery pump atmaximum-relief valve pressure even when no actuating fluid is demandedby the system.- This, in turn, results in an undesirable, excessiveamount of heat generation in the hydraulic system.

Also, separate and apart from the problem of wasted engine horsepowerand undesirable heat generation resulting from operation of the pump atthe neutral or noload condition, there is the problem of cooling systemoverloading caused by continued operation of the pump at the maximumdisplacement position even after a predetermined maximum pressure isreached. This requires corrective action in the form of returning thepump to its minimum displacement position upon attaining thepredetermined maximum'pressure.

It is to a solution of these and other problems that the invention ofthis disclosure is directed.

It is, therefore,an object of this invention to provide a variabledisplacement pump having pressure compensator control means operable tocontrol pump displacement in response to system pressure.

It is alsoan object of this invention to provide a variable displacementpump having pressure compensator control means which functions to savehorsepower and prevent excessive heat generation and stalling of thedriving engine when one or more hydraulic implement circuits areactuated.

It is also an object of this invention to provide a variabledisplacement pump having pressure compensator control means toautomatically set pump displacement at some predetermined minimumdisplacement or flow condition when the hydraulic implement circuits serviced by the pump are in a neutral condition, thereby limitinghorsepower loss and preventing excessive heat generation.

It is a still further object of this invention to provide a variabledisplacement. pump having pressure compenstor control means toautomatically change the pump displacement from maximum to minimum whenthe system pressure reaches a predetermined maximum value, therebylimiting horsepower loss and preventing excessive heat generation.

It is a still further object of this invention to provide a variabledisplacement pump having a pressure compensator control means utilizingpilot operation for controlling pump displacement whereby more stabilityand less hunting and overshoot are encountered when a change indisplacement is required.

It is a still further object of this invention to provide a variabledisplacement pump having pressure compensator control means in the formof interchangeable cap- 'sules whereby pump flow direction may bechanged by merely interchanging capsules.

It is yet another object of this invention to provide a variabledisplacement pump having pressure compensator control means operable toprovide sharp cutoff of pump flow when the hydraulic implement circuitsserviced by the pump are in a neutral condition or the system pressurereaches a predetermined maximum value.

Other objects and advantages of the present invention will becomeapparent from the following description and claims as illustrated in theaccompanying drawings which, by way of illustration only, show apreferred embodiment of the present invention and the principles ofoperation thereof. It is to be understood that the scope of theinvention is not to be limited thereto, but is to be determined by thescope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1' is a top plan view of ahydraulic, variable displacement pump having hydraulic pressurecompensator control means installed therein;

DETAILED DESCRIPTION OF THE INVENTION 7 Referring now to FIG. 1, thereis shown generally at 10 a top view of a variable displacement pumpcontaining two vertical bores 12, 14 which are offset from the pumpcenter line. These bores contain the mechanisms for changing the pumpdisplacement, as will be hereinafter described. The pump body consistsof a head 16 seated upon a housing 18. Contained within the head is aninlet passage 20 and an outlet passage 22.

Referring now to FIG. 2, there is showna vertical, cross-sectional viewof variable displacement pump 10 taken along line lI-II in FIG. 1. Apump cylinder barrel 24, having a plurality of axially-oriented bores 26and a plurality of reciprocably-mounted pistons therein, is locatedwithin the pump housing. The pistons are guided by a slipper pad 28rotatably, slidably mounted on support means in the form of anonrotatable but tiltable swash plate 30. The swash plate is pivotableabout a transverse axis by means of transverse pivot pins (not shown)retained in transverse bores (not shown) in the sides of housing 18.

The angle of tilt of the swash plate 30 with respect to the axialdirection of the bores 26 determines thev amount of stroke ordisplacement of the pistons 32 within their respective bores 26 in theconventional manner. Since slipper pad 28 is ball-and-socket-jointconnected to pistons 32 which, in turn, ride on surface 34 of the swashplate, it can be seen that if the swash plate were rotated clockwiseabout its pivot point from the position shown, the reciprocating actionof the pistons in their respective bores would be minimized. Thus, aminimum displacement of fluid would occur through outlet passage 22 byway'of kidney port 36.

The operation of the invention is as follows. When all of the implementcontrol valves on a machine (not shown) utilizing the invention are in aneutral condition, a pilot line 38 will be open to tank. Prior to pumpcylinder barrel rotation, the swash plate 30 is swivelled as shownagainst maximum displacement stop 40 by means of a piston 42 which isbiased by a spring 44 which, in turn, reacts against a housing 46 ofcartridge assembly 48. A flange 50 on cartridge assembly 48 securelylocates the assembly between the pump head 16 and pump housing 18. Theentire assembly is secured in place within the pump body by means of anut 52 which abuts against the top surface of head 16.

When the pump cylinder barrel 24 starts to rotate by means of shaft 54connected to the engine or other power means (not shown), and an outputfluid flow will be generated along with an output fluid pressure. Thisoutput flow .and pressure will be communicated from axial bores 26through kidney port 36 and into passage 56. From this passage thepressure will be intercommunicated with chamber 58 formed on the end ofa spool 60, by way of an annulus 62 and a passage 64. Fluid will thenflow through axial passage 66 and orifice 68 of spool 60 and into achamber 70 and then to tank by way of passage 72, annulus 74 and pilotline 38.

This will cause spool 60 to shift upwardly from the position shown dueto the differential pressure created by fluid flowing through orifice68. The upward movement of spool 60 will compress spring 76 until thespool communicates annular groove 78 thereon with an annulus 80. Thiswill vent chamber 82, wherein piston 42 is reciprocally located, to tankby way of passage 84, annulus 80, annular groove 78, and line 86 by wayof passage 88. At the same time, pump pressure in passage 56, annulus 62and kidney port 36 will be communicated to an annulus 90 via a passage92. Pressure will be then communicated into passage 94 contained incartridge 96 of the cartridge or capsule assembly generally shown at 98.A flange 100 on the cartridge securely locates the assembly between thepump head 16 and the pump housing 18.

Fluid under pressure in passage 94 is directed to a chamber 102 where itworks against a piston 104. The force of the pressure acting on piston104 will cause the piston to move downwardly. Since the piston is incontact with an arm extension 106 of swash plate 30, the swash platewill be swivelled in a clockwise direction toward its minimumdisplacement position. This minimum displacement position would beachieved when the extension 106 contacts adjustable minimum displacementstop 108. This clockwise rotation of the swash plate 30 will occuragainst the biasing force of spring, piston combination 44, 42 which isacting upon the opposite arm extension 110 of the swash plate. Theposition of the extension 106 against adjustable stop 108 corresponds topoint A in the graph of FIG. 3. At this minimum displacement position,pump flow and pressure will be at a minimum, which will result in lesshorsepower loss and less heat generation in the system.

When one or more of the control valves on the machine are activated,line 38 will be blocked from tank by means (not shown) such that thepressures in chambers 58 and will equalize and spool 60 will be moveddownwardly by the influence of biasing spring 76 to the position shownin FIG. 2. In this position, system pressure is directed to passage 66,a passage 112 transversely intersecting passage 66, annulus 80, passage84, and then into chamber 82. Since the area of piston 42 in chamber 82is greater than the area of piston 104 in chamber 102, piston 42 willpush downwardly on the swash plate extension until it is stopped at themaximum displacement position by stop 40.

When this occurs, pump flow and pressure will correspond to point B onthe graph of FIG. 3. The pressure within the circuit will then rise inproportion to the load placed on the circuit, while pump flow is heldconstant as represented by the line B-C on the graph. When the systempressure reaches a predetermined maximum, as shown by point C on thecurve of FIG. 3, a poppet valve 114 (as seen in FIG. 2) will openagainst the biasing force of a spring 116, thus venting chamber 70 totank by way of passage 118 and line 120.

This operation also allows fluid to flow through orilice 68, which willresult in a differential pressure to move spool 60 upwardly to ventchamber 82, as previously described. This action will allow theoperating pressure in chamber 102 to overcome the pressure in chamber 82and will swivel the pump back to the minimum displacement positioncorresponding to point D on the graph of FIG. 3. This swivelng of theswash plate will cause the sharp cutoff of pump flow along the almostvertical line C-D. As is well known in the art, very low flow and highpressure (D) will result in much less heat generation and horsepowerloss than will high flow at high pressure (C).

Turning to FIG. 2, pump rotation will be in one direction due to thefact that the swash plate can be swivelled only in a clockwisedirection. Therefore, when pump flow direction is to be changed, thecapsule or cartridge assemblies 98 and 122 must also be interchangedalong with stops 40 and 108 in order that the inlet and outlet portswill remain the same. This interchanging may be easily accomplished withthe device of the instant invention, since cartridge assemblies 98 and122 have the same exterior circumferential dimension as well as beinggenerally cylindrical.

In addition, and to facilitate this interchanging, the locations anddimensions of the leftmost annuli 62, 74, duplicate those of therightmost annuli 90, 124, respectively. More particularly, annulus 74 islocated at the same vertical level in the head as annulus 124 wherebyinterchanging of assemblies 98 and 122 results in passage 72 incartridge assembly 48 being in fluid communication with tank line 38 byway of the annuli and passages 126, 128 and chamber 130. Access to thechamber 130 may be conveniently had by means of plug 132 which isthreadably secured in the top surface of head 16.

Similarly, annuli 62 and 90 are located at the same vertical level inthe head. Passage 134 and line 136 leading to tank are provided so as tocorrespond with their counterparts numbered 88, 86. Obviously, when theassemblies are located as shown in FIG. 2, cartridge 96 obturatespassage 134 and annulus 124 whereby these elements are unused.

To interchange the assemblies, head 16 is removed from housing 18 bydetaching fastening means (not shown). Threaded plug 138 is unscrewedfrom its mating opening in the end of cartridge 96 and nut 52 issimilarly unscrewed from the threaded end of assembly 48. The respectivecartridges are interchanged, plug 138 and nut 52 resecured, and the head16 resecured to housing 18. As aforementioned, an intermediate stepofexchnaging stops 40 and 108 would also be accomplished.'

It is to be understood that the foregoing description is merelyillustrative of a preferred embodiment of the invention, and that thescope of the invention is not to be limited thereto, but is to bedetermined only by the scope of the appended claims.

What is claimed is:

l. A variable displacement axial piston pump of the type having ahousing means containing an inlet port and a discharge port, a pluralityof piston means and an angularly adjustable swash plate means fordetermining piston displacement and thereby the amount of fluiddischarged from the pump, resilient means in a first cartridge assemblymeans biasing the swash plate means to its maximum discharge positionwhereby a maximum of fluid is displaced by-the pump, and pressureresponsive means in a second cartridge assembly means for shifting saidswash plate means to its minimum discharge position in responseto apressure such as from a hydraulic system, reversing means wherebyinterchanging said first cartridge assembly means with said secondcartridge assembly means causes the pump flow direction to be reversed,said reversing means comprising a pair of stop means, one of which isassociated with the swash plate adjacent said first cartridge assemblymeans and the other of which is associated with the other of saidcartridge assembly means, said stop means being interchangeable, onewith the other, said first cartridge assembly means comprising a firstgenerally cylindrical cartridge member in a first bore in said housingmeans, said second cartridge assembly means comprising a secondcartridge member in a seond bore in said housing, and wherein said firstand second cartridge members are dimensioned so as to permitinterchanging of said cartridge members in said bores, said secondcartridge member comprising a generally elongated member and saidpressure-responsive means comprising a first reciprocable pistonextending from a bore in one end of said cartridge member and therebydefining a first chamber therein, said first cartridge member being agenerally elongated member and wherein said resilient means in saidfirst cartridge member comprises a second reciprocable piston extendingfrom a reciprocable bore in one end of said cartridge member and therebydefining a second chamber therein, and further including spring means insaid second chamber biasing said piston outwardly from said bore, andfurther including a pilot line in said housing adapted to sense pressurefrom a hydraulic system and wherein said means for suddenly shiftingsaid swash plate to its minimum discharge position compriss spool meansresponsive to line pressure for directing pressure fluid to said firstchamber so as to cause said first reciprocable piston to tilt said swashplate means to the minimum discharge position, and wherein said spoolmeans compriss a spool contained in a bore and defining a third chamberat one end of said bore, and further including poppet valve means forrelieving excessive pressure occurring in said third chamber.

1. A variable displacement axial piston pump of the type having ahousing means containing an inlet port and a discharge port, a pluralityof piston means and an angularly adjustable swash plate means fordetermining piston displacement and thereby the amount of fluiddischarged from the pump, resilient means in a first cartridge assemblymeans biasing the swash plate means to its maximum discharge positionwhereby a maximum of fluid is displaced by the pump, and pressureresponsive means in a second cartridge assembly means for shifting saidswash plate means to its minimum discharge position in response to apressure such as from a hydraUlic system, reversing means wherebyinterchanging said first cartridge assembly means with said secondcartridge assembly means causes the pump flow direction to be reversed,said reversing means comprising a pair of stop means, one of which isassociated with the swash plate adjacent said first cartridge assemblymeans and the other of which is associated with the other of saidcartridge assembly means, said stop means being interchangeable, onewith the other, said first cartridge assembly means comprising a firstgenerally cylindrical cartridge member in a first bore in said housingmeans, said second cartridge assembly means comprising a secondcartridge member in a seond bore in said housing, and wherein said firstand second cartridge members are dimensioned so as to permitinterchanging of said cartridge members in said bores, said secondcartridge member comprising a generally elongated member and saidpressureresponsive means comprising a first reciprocable pistonextending from a bore in one end of said cartridge member and therebydefining a first chamber therein, said first cartridge member being agenerally elongated member and wherein said resilient means in saidfirst cartridge member comprises a second reciprocable piston extendingfrom a reciprocable bore in one end of said cartridge member and therebydefining a second chamber therein, and further including spring means insaid second chamber biasing said piston outwardly from said bore, andfurther including a pilot line in said housing adapted to sense pressurefrom a hydraulic system and wherein said means for suddenly shiftingsaid swash plate to its minimum discharge position compriss spool meansresponsive to line pressure for directing pressure fluid to said firstchamber so as to cause said first reciprocable piston to tilt said swashplate means to the minimum discharge position, and wherein said spoolmeans compriss a spool contained in a bore and defining a third chamberat one end of said bore, and further including poppet valve means forrelieving excessive pressure occurring in said third chamber.